1. Field of the Invention
The present invention generally relates to a method for depositing a ferromagnetic compound, such as chromium dioxide (CrO.sub.2), in thin film form in a selective fashion over a substrate, such that the growth occurs only above specific regions of the substrate that have been appropriately modified.
More specifically, the invention relates to a method for depositing such a ferromagnetic compound in a selective growth process for a plurality of applications including magnetic memory and storage-based devices, as well as other devices.
2. Description of the Related Art
Conventional systems utilize chromium dioxide (CrO.sub.2) as an important ferromagnetic material which is used, for example, as a particulate magnetic recording media. Chromium dioxide has the rutile crystal structure which is tetragonal with lattice parameters of a=4.423 .ANG. and c=2.917 .ANG.. The chromium ions are in the Cr.sup.+4 state with the electronic configuration [Ar]3d.sup.2 with a magnetic moment of 2 .mu..sub.B per ion.
Because of its half-metallic nature, where the majority spin electrons have a metallic character and the minority spin electrons have a semiconducting character (e.g., see K. Schwarz, J. Phys. F 16, 211 (1986)), chromium dioxide also is ideally suited for use in magnetic tunnel junction (MTJ) devices. Suitable applications for CrO.sub.2 include, as a media for magnetic storage, and as a component in magnetic tunnel junction devices.
Recently, there have been attempts to deposit CrO.sub.2 in the form of thin films (though not in a selective area fashion), as described, for example, in R. C. DeVries, "Epitaxial Growth of CrO.sub.2 ", Mat. Res. Bull. 1, 83 (1966); S. Ishibashi, T. Namikawa, and M. Satou, "Epitaxial Growth of CrO.sub.2 in Air", Japan J. Appl. Phys. 17, 249 (1978); S. Ishibashi, T. Namikawa, and M. Satou, "Epitaxial Growth of Ferromagnetic CrO.sub.2 Films in Air", Mat. Res. Bull. 14, 51 (1979); and K. P. Kamper, W. Schmitt, G. Guntherodt, R. J. Gambino, and R. Ruff, "CrO.sub.2 --A New Half-Metallic Ferromagnet?", Phys. Rev. Lett. 59, 2788 (1987).
However, these studies have been confined to the uniform deposition of CrO.sub.2 that covered the entire substrate (e.g., a substantially continuous deposition). Further, selective area growth of CrO.sub.2 has not been attempted on predetermined locations (e.g., those that could be patterned) on the substrate surface with arbitrary size dimensions. Thus, control in the deposition of such films has been limited, and thus the applications of such films have been limited.
Selective area growth, which consists of depositing a material over a substrate in such a fashion that material is deposited only on specific regions of substrate that have been appropriately modified, is an established technique in the field of compound semiconductors and metal deposition.
In the area of semiconductor deposition, selective growth has been used for the production of higher quality thin film optoelectronic devices for making better light emitters, and in the case of metals, selective growth has been used for different applications such as plugs for hole filling in Si technology. The particular technical details for selective area growth of various systems are quite diverse due to the different chemistries involved.
Thus, as noted above, selective area growth has not been used for applications in ferromagnetic thin films or in forming any substrates used in magnetic memory applications, for example.
The conventional method of patterning blanket thin films using photolithography and etching is difficult in the case of CrO.sub.2 since it is not readily etched in a reactive plasma or with wet chemicals. Hence, selective area growth would be a preferred approach since it requires no subsequent patterning steps.